This invention relates to methods of making abrasive articles in which abrasive particles are bonded to a substrate by a binder. In particular the invention relates to methods of making coated abrasive and nonwoven, fibrous abrasive articles.
Conventional coated abrasive articles have an abrasive layer of abrasive particles and binder attached to a backing material. In one common form the abrasive layer includes make and size layers of binder. Such coated abrasive articles are typically made by applying a the make layer (e.g., a resin) onto a major surface of the backing material, at least partially embedding abrasive particles into the make layer, at least partially solidifying (e.g., curing) the make layer, applying the size layer (e.g., a resin) over the abrasive particles and make layer, and solidifying (e.g., curing) the size layer. One function of the size layer is to improve the retention of the abrasive particles to the backing material.
Coated abrasive articles optionally further include other layers known in the art, including presize, backsize, tie, and supersize layers Functions of additional layers include providing a grinding aid, lubricant, or antistat.
Conventional nonwoven abrasive articles are typically made of nonwoven webs constituted of a network of synthetic fibers or filaments which provide surfaces upon which abrasive particles are adhesively attached by a binder.
Nonwoven abrasive articles have employed a xe2x80x9cmakexe2x80x9d coat of resinous binder material in order to secure the abrasive particles to the fiber or filament surface backing as the particles are oriented on the backing or throughout the lofty fibrous mat. A xe2x80x9csizexe2x80x9d coat of resinous binder material also has been applied over the make coat and abrasive grains in order to anchor and reinforce the bond of the abrasive particles to the backing or fibrous mat. A conventional sequence of fabrication steps for making nonwoven abrasive articles involves: first applying the make coat and abrasive particles to the backing or lofty fibrous mats; partially curing the make coat; applying the size coat; and finally, the make and size coats are fully cured.
In another known process for the production of nonwoven abrasive articles a pre-bond coat is applied to the fibrous mat followed by a make coat which contains abrasive particles. The pre-bond coat may be applied by roll coating and the make coat by spraying each side of the web.
Binder resin used to make the abrasive articles are frequently the same or similar to avoid compatibility problems potentially associated with the use of dissimilar resins. Exemplary details regarding binders for abrasive articles can be found, for example, in U.S. Pat. No. 5,980,597 (Loughlin) and U.S. Pat. No. 5,478,908 (Hesse et al.). Thermally curable binders are one type of resin that has been used to make coated abrasives and nonwoven fibrous abrasive articles as they tend to provide abrasive articles having excellent properties (e.g., enhanced heat resistance). Conventional thermally curable resins include phenolic resins, urea formaldehyde resins, urethane resins, melamine resins, epoxy resins, and alkyd resins. Among these, phenolic resins have been used extensively to manufacture abrasive articles because of their thermal properties, availability, low costs and ease of handling. To render the resin precursors coatable, obtain the proper coating viscosities, and obtain defect free coatings, solvents are commonly added to the uncured resins.
There are two basic types of conventional phenolic resins: resole and novolac phenolic resins. Novolac phenolic resins are characterized by being acid catalyzed and having a ratio of formaldehyde to phenol of less than one, typically between 0.5:1 to 0.8:. Acidic catalysts suitable for novolac phenolic resins include sulfuric, hydrochloric, phosphoric, oxalic, and p-toluene sulfonic acids. Novolac phenolic are thermoplastic resins and in the cured form are brittle solids. Novolac phenolic resins are typically reacted with other chemicals to form a crosslinked solid. Resole phenolic resins are characterized by being alkaline catalyzed and having a ratio of formaldehyde to phenol of greater than or equal to one, typically from 1:1 to 3:1. Alkaline catalysts suitable for resole phenolic resins include sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines, or sodium carbonate. Resole phenolic resins are thermosetting resins and in the cured form exhibit excellent toughness, dimensional stability, high strength, hardness, and heat resistance.
In formulating the phenolic resins, the monomers currently used in greatest volume are phenol and formaldehyde. Other noteworthy starting materials are the alkyl-substituted phenols, including cresols, xylenols, p-tert-butyl-phenol, p-phenylphenol and nonylphenol. Diphenols e.g. resorcinol (1,3-benzenediol and bisphenol-A (bis-A or 2,2-bis(4-hydroxyphenyl)propane) are employed in smaller quantities for applications requiring special properties.
In the production of adhesive coatings for nonwoven abrasive articles, one standard starting phenolic resin composition is a 70% solids condensate of a 1.96:1.0 formaldehyde: phenol mixture with 2% potassium hydroxide catalyst added based on the weight of phenol. The phenolic component of the phenolic resin is typically solid and requires the addition of solvent to render it soluble to react with the formaldehyde. The phenolic resin composition is typically 25 to 28% by weight water and 3 to 5% by weight propylene glycol ether to reduce the viscosity of the resin. Before this resin is used as a make or size coat, (i.e. to make it coatable), further viscosity reduction is often achieved using VOC (i.e. a volatile organic compound). A conventional phenolic resin make coat may contain up to 40% by weight of a VOC, such as isopropyl alcohol to reduce viscosity and make the phenolic compatible with resin modifiers (flexibilizers), while a size coat might contain up to 20% % by weight of a VOC, such as diethylene glycol ethyl ether. Unreacted phenol and formaldehyde in the final, cured resin also contribute to VOC.
To reduce emissions of VOC, progress has been made to modify suitable resin systems to replace organic solvents with water (see, e.g., U.S. Pat. No. 5,178,646 (Barber et al.) and U.S. Pat. No. 5,306,319 (Krishnan et al.)).
Although bisphenol/formaldehyde resin systems may have acceptable VOC levels, the use of these resins as make, size and pre-bond coats in abrasive articles does not provide abrasive articles having performance characteristics equivalent to abrasive articles having make, size and pre-bond coats of phenol/formaldehyde resins, particularly when coarse abrasive particles are used.
In one aspect, the present invention an abrasive article (e.g., a coated abrasive article or a nonwoven abrasive article) comprising abrasive particles bonded to a substrate by a bond system, wherein at least a portion of the bond system comprises a reaction product of components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
In another aspect, the present invention comprises an abrasive article comprising abrasive particles bonded to a substrate by a bond system, wherein at least a portion of the bond system is derived by curing a mixture of a resole phenolic resin and a bisphenol/formaldehyde resin.
In yet another aspect, the abrasive article comprises abrasive particles bonded to a substrate by a bond system wherein at least a portion of the bond system comprises polymeric material preparable by combining components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
In some embodiments of the present invention, the abrasive article is a coated abrasive comprising a backing material, a make coat having abrasive grains therein, and a size coat over the abrasive grains, wherein at least one of the make coat or size coat comprises the bond system. In other embodiments of the present invention, the abrasive article is a nonwoven abrasive article comprising a nonwoven web constituted of a network of synthetic fibers of filaments which provide surfaces on which abrasive particles are attached thereto by the bond system.
In another aspect, the present invention provides methods for making the abrasive articles. For example, one method comprises"" applying a curable bond system (see, e.g., descriptions above) and abrasive particles to a substrate; and curing the bond system. Further, for coated abrasive articles, for example, the method comprises applying a make coat to a major surface of a backing material, at least partially embedding abrasive particles to the make coat, and applying a size coat over the abrasive particles, wherein at least one of (preferably, both) the make coat or size coat is prepared, or is preparable, by mixing components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
For making nonwoven abrasive articles, for example, the method can comprise applying a make coat and abrasive particles to the nonwoven web, and applying a size coat over the abrasive make coat and abrasive particles, wherein at least one of (preferably, both) the make coat or size coat is prepared, or is preparable, by mixing components comprising a resole phenolic resin and a bisphenol/formaldehyde resin.
According to the present invention there is provided a method of forming an abrasive article comprising applying a curable bond system and abrasive particles to a substrate and curing the bond system wherein at least a portion of the bond system is derived from a mixture of a resole phenolic resin and a bisphenol/formaldehyde resin.
Also according to the invention there is provided the resole phenolic resin and bisphenol/formaldehyde resin are mixed as aqueous alkaline dispersions.
Surprisingly, it has been found that the mixture of a resole phenolic resin and a bisphenol/formaldehyde resin (hereinafter BisP) provides low emission coating formulations while maintaining the performance level associated with the use of a resole phenolic resin. Furthermore, the reduction in emission from the coated mixture compared with the use of the resole phenolic resin alone is significantly more than would be expected based upon the emissions of the resole phenolic resin and BisP resin. It appears that the two resins interact positively for lower emissions with the BisP resin reducing the phenol emission and acting as a formaldehyde scavenger.
The resole phenolic resins used in the invention comprise phenol and formaldehyde. The molar ratio of formaldehyde to phenol is greater or equal to 1, typically in the range 1:1 to 3:1. The reaction between the formaldehyde and phenol components is catalyzed by alkaline catalysts such as sodium hydroxide, barium hydroxide, potassium hydroxide, calcium hydroxide, organic amines and sodium carbonate. The coating formulations are generally preferred as aqueous dispersion e.g. 30 to 95% solids, preferably 60 to 80% solids) with the catalyst dissolved in the water. Typically the coating formulations comprise 2% by weight of catalyst.
The BisP resin is derived from a compound having the formula: 
in which:
R represents a substituted or unsubstituted alkyl group, particularly a group having from 1 to 6 carbon atoms. The most frequently encountered examples of such bisphenols are bisphenol F wherein the R group is xe2x80x94CH2xe2x80x94; and bisphenol A wherein the R group is C(CH3)2xe2x80x94
The preferred bisphenol components used to make the binders for the process of the invention have formulae in which the group R has form 1 to 4 carbon atoms and is most preferably unsubstituted.
These bisphenols react with formaldehyde in a base catalyzed reaction in the same way as phenol except for the presence of two phenolic hydroxyl groups on the molecule rather than one. The BisP resins are compatible with phenol/formaldehyde resins.
Suitable BisP resins are available from Oxychem and bear the CAS number 25085-75-0. The resin formulation generally comprises from 70 to 75% solids of the resin (measured after standing at 135xc2x0 C. for three hours) in an aqueous medium and have a viscosity at 25xc2x0 C. of 1100 to 1300 cP.
Another suitable resin is commercially available under the trade designation xe2x80x9cBAKELITE 9353SWxe2x80x9d and is available at 57% solids.
The phenolic group/formaldehyde ratios of the BisP are generally equivalent to those used in conventional phenol/formaldehyde resins. Also the useful amount of base catalyst (usually an alkali metal hydroxide) is calculated on an equivalent basis to that used in phenol/formaldehyde resins. The curing proceeds by the same route an at roughly the same temperatures that are conventional for phenol/formaldehyde resins.
The resin mixture used in the invention generally comprises from 30 to 80% by weight solids of resole phenolic resin and from 20 to 70% by weight solids of BisP resin. The precise ratio will depend upon the type of abrasive product and whether the resin mixture is used as a make or size coat etc. For coated abrasive products the resin mixture preferably comprises from 55 to 70% weight solids, more preferably 65 to 70% resole phenolic resin and correspondingly from 30 to 45% weight solids, more preferably 30 to 35% weight solids BisP. Suitable resin mixtures for the production of lofty nonwoven abrasive articles may comprise from 40 to 60%, preferably about 50% by weight solids of resole phenolic resin and correspondingly from 60 to 40%, preferably about 50% by weight solid of BisP.
In addition to the alkaline catalysts the coating formulations of the resin mixture may comprise other ingredients known in the art including solvents, plasticisers, fillers, fibers, lubricants, grinding aids, wetting agents, surfactants, pigments, dyes, coupling agent, suspending agent and reactive diluents. Preferably the resin mixture is used in both the size and make coats.
The construction and general methods of making coated abrasives are well known in the art and may be used in the subject invention since the resin mixture is compatible with the known phenolic resin systems used in the art. Thus, the selection of backing material, abrasive particles, use of primer coats, supersize coats and additives used in known coated abrasives are all envisaged for use in the subject invention. Examples of suitable abrasive particles include fused aluminum oxide (including white fused alumina, heat-treated aluminum oxide and brown aluminum oxide), silicon carbide, boron carbide, titanium carbide, diamond, cubic boron nitride, garnet, fused alumina-zirconia, and sol-gel-derived abrasive particles, and the like. The sol-gel-derived abrasive particles may be seeded or non-seeded. Likewise, the sol-gel-derived abrasive particles may be randomly shaped or have a shape associated with them, such as a rod or a triangle. Examples of sol gel abrasive particles include those described U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 5,011,508 (Wald et al.), U.S. Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer), U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,498,269 (Larmie), and U.S. Pat. No. 5,551,963 (Larmie), the disclosures of which are incorporated herein by reference. Additional details concerning sintered alumina abrasive particles made by using alumina powders as a raw material source can also be found, for example, in U.S. Pat. No. 5,259,147 (Falz), U.S. Pat. No. 5,593,467 (Monroe), and U.S. Pat. No. 5,665,127 (Moltgen), the disclosures of which are incorporated herein by reference. In some instances, blends of abrasive particles may result in an abrasive article that exhibits improved grinding performance in comparison with abrasive articles comprising 100% of either type of abrasive particle
Further details regarding coated abrasive products can be found, for example, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No. 4,737,163 (Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat. No. 5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S. Pat. No. 5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follett et al.), U.S. Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5, 609,706 (Benedict et al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat. No. 5,954,844 (Law et al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.), and U.S. Pat. No. 5,975,988 (Christinason), the disclosures of which are incorporated herein by reference. Further details regarding bonded abrasive products can be found, for example, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,741,743 (Narayanan et al.), U.S. Pat. No. 4,800,685 (Haynes et al.), U.S. Pat. No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,038,453 (Narayanan et al.), U.S. Pat. No. 5,110,332 (Narayanan et al.), and U.S. Pat. No. 5,863,308 (Qi et al.), the disclosures of which are incorporated herein by reference. Further, details regarding vitreous bonded abrasives can be found, for example, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,898,597 (Hay), U.S. Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,094,672 (Giles et al.), U.S. Pat. No. 5,118,326 (Sheldon et al.), U.S. Pat. No. 5,131,926 (Sheldon al.), U.S. Pat. No. 5,203,886 (Sheldon et al.), U.S. Pat. No. 5,282,875 (Wood et al.), U.S. Pat. No. 5,738,696 (Wu et al.), and U.S. Pat. No. 5,863,308 (Qi), the disclosures of which are incorporated details regarding nonwoven abrasive products can be found, for example, in U.S. Pat. No. 2,958,593 (Hoover et al.), the disclosure of which is incorporated herein by reference.
The method of making a nonwoven abrasive article according to the present invention may comprise, for example, applying a pre-bond coat to said nonwoven web and thereafter applying a make coat and abrasive particles. Preferably, the blend is used in the make and size coats or the pre-bond and make coats of the nonwoven abrasive article.
The resin mixtures are compatible with the existing bonding systems used in the production of nonwoven abrasive articles and the known construction, ingredients and processes are for making these abrasive articles may be employed in accordance with the subject invention. Examples of such processes are disclosed in U.S. Pat. No. 2,958,593 (Hoover et al.) and U.S. Pat. No. 5,178,646, (Barber et al.), the disclosures of which are herein incorporated by reference.
This invention is further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention. Various modifications and alterations of the invention will become apparent to those skilled in the art. All parts and percentages are by weight unless otherwise indicated.
In the following Examples:
Resole A: 75% by weight solids aqueous dispersion of resole phenolic resin with a formaldehyde/phenol ratio of approximately 2.0/1 and a pH of about 8.7 and a viscosity of about 2100 cP at 25xc2x0 C. as measured using a Brookfield RV viscometer available from Georgia-Pacific Resins, Inc. Columbus, Ohio.
Resole B: 75% by weight solids aqueous dispersion of resole phenolic resin with a formaldehyde/phenol ratio of approximately 2.0/1 and a pH of 8.5 and a viscosity of about 1900 cP at 25xc2x0 C. as measured using a Brookfield RV viscometer, being of lower catalyst content than Resole A, available from Georgia-Pacific Resins, Inc. Columbus, Ohio.
Resole C: 71% by weight solids aqueous dispersion of resole phenolic resin with a formaldehyde/phenol ratio of approximately 2.0/1, a pH of about 8.5 and a viscosity of about 1400 cP at 25xc2x0 C. as measured using a Brookfield RV viscometer, having higher molecular weight than either Resole A and B and containing about 5% by weight of urea, available from Georgia-Pacific Resins, Inc., Columbus, Ohio.
BisP: 57% aqueous dispersion of bisphenol/formaldehyde resin commercially available under the trade designation xe2x80x9cBAKELITE SW9353xe2x80x9d, available from Bakelite AG, Iserlohn, Germany.
Emulan A: an ethoxylated oleic acid surfactant, available from BASF Corp., Ludwigshafen, Germany
Irgastat: a liquid polyethylene glycolester surfactant, available from Ciba-Geigy Corp., Hawthorne, N.Y.
Iron oxide dispersion: a 50% by weight solids aqueous dispersion of iron oxide pigment, available from Penn Color, Inc., Doylestown, Pa.
Bordeau Dye: an aqueous dispersion comprising, by weight, 23% isopropanol, 10% red pigment, 2% by pigment (xe2x80x9cNIGROSINExe2x80x9d), 10% water and 55% Resole C, available from Wilson Color Co., Neshamic Station, N.J.
Calcium carbonate: a filler, available from ECC International, Sylacauga, Ala.
Titanium dioxide: a filler, available from Kemira Pigments, Inc., Oklahoma City, Okla.